The codling moth (Cydia pomonella) is a member of the Lepidopteran family Tortricidae. They are known as an agricultural pest, their larva being the common apple worm or maggot. It is native to Europe and was introduced to North America, where it has become one of the regular pests of apple orchards. It is found almost worldwide. It also attacks pears, walnuts, and other tree fruits. This larva is the famous “worm in the apple” of cartoon and vernacular frame; it is not related to the earthworm.
Codling moths have accounted for more damage to apples then any other pest. Their unique biology combined with their physical attributes makes them forever a formidable foe to
anyone that grows apples. Whether one has one tree or an orchard spanning hundreds of acres, codling moths can take away an entire harvest quickly and consistently
Codling moths actually don't cause any damage. In fact, like many other insects, it's their larva which do all the bad deeds. Codling moths overwinter in the pupa stage and emerge in the spring when local temperatures are right.
The codling moth is greyish with light grey and copper stripes on its wings, and has an average wingspan of 17 mm. The females lay eggs on fruit or leaves and the black-headed yellow larvae attack the fruit immediately upon hatching. Each larva burrows into the fruit, eats for around three weeks, then leaves the fruit to overwinter and pupate elsewhere. Most nourishment is obtained by feeding on the proteinacous seeds.
The codling moth is bivoltine in most regions of the USA—in the Pacific Northwest there is a partial third generation.
Codling moth adults are about ½ to ¾ inch long with mottled gray wings that are held tentlike over their bodies. Their appearance blends well with most tree bark, making them difficult to detect. The larvae are white to light pink “worms” with a dark brown head. They are one of the few worms that are likely to be found inside pear or apple fruit. Navel orange worms may also be found in walnuts, but these can be distinguished from codling moth larvae by the crescent-shaped markings on the second segment behind the orange worm head and by the excess webbing that they leave in the nut. On apples and pears, larvae penetrate into the fruit and tunnel to the core, leaving holes in the fruit that are filled with reddish-brown crumbly droppings called frass. If left uncontrolled, they can cause substantial damage, often infesting 20 to 90% of the fruit, depending on the variety and location. In walnuts, the larvae feed on the kernels. Nuts damaged early in the season when the nuts are quite small will drop off trees soon after damage occurs. Nuts damaged later in the season will remain on trees, but their kernels are inedible. Walnuts are not as favored a host as apples and pears and untreated trees may incur very little to modest damage (10 to 15% of the nuts), depending on variety and location.
Codling moths overwinter as full-grown larvae within thick, silken cocoons under loose scales of bark and in soil or debris around the base of the tree. The larvae pupate inside their cocoons in early spring and emerge as adult moths mid-March to early April. The moths are only active a few hours before and after sunset and they mate when the sunset temperatures exceed 62° F. After mating each female deposits 30 to 70 tiny, disc-shaped eggs singly on fruit, nuts, leaves, or spurs. After the eggs hatch, young larvae seek out and bore into fruit or developing nuts. After completing development they leave the fruit and drop from the trees to search out pupation sites and continue the life cycle in the soil or on debris under the tree; some crawl back up the tree to pupate in bark crevices. The rate of development will vary with temperature, proceeding more rapidly in warmer weather and climates. Depending on the climate, codling moth can have two, three, and sometimes four, generations per year.
Codling moth can be very difficult to manage, especially if the population has been allowed to build up over a season or two. It is much easier to keep moth numbers low from the start than to suppress a well-established population. In trees with low to moderate levels, codling moth can often be kept to tolerable levels by using a combination of nonchemical management methods; however, it is important to begin implementing these measures early in the season.
Where populations are high and many infested trees are nearby, insecticide applications may be necessary to bring populations down to low levels. However, to be effective, the timing of insecticide spray applications is critical and are difficult to time accurately. In most backyard situations, the best course of action may be to combine a variety of the nonchemical and/or low toxicity chemical methods discussed below and accept the presence of some wormy fruit.
There are several known methods of controlling codling moths. These include:
Nonchemical Control
There are several methods for reducing codling moth that do not require the use of insecticides. Selecting varieties that are less susceptible to damage, such as early maturing apples and pears and late leafing walnuts, can greatly reduce the potential for damage.
Once trees are planted, the most effective nonchemical control methods include sanitation, mass trapping, trunk banding, and fruit bagging. All of these methods are described below. Pruning trees to a height where the canopy is easy to reach also will facilitate nonchemical management of this pest.
If a backyard tree or orchard has a very high moth population, it may take several seasons diligently practicing these nonchemical control methods to reduce codling moth damage to about 10 to 20% of fruit infested. Nearby orchards or backyard trees in which no control program is in place can serve as a continual source of codling moths, thus making it even more difficult to limit damage through nonchemical means alone.
Sanitation.
Sanitation should be the first step in any codling moth control program and it is even more important for those wishing to use primarily nonchemical management approaches. Combining sanitation with mass trapping (see below) may be all that is required in an isolated site with low codling moth populations. However, in areas with high populations or nearby unmanaged host trees, sanitation will probably need to be combined with more aggressive methods to achieve satisfactory control.
Every week or two, beginning about 6 to 8 weeks after bloom, the fruit on trees must be checked for signs of damage. Infested fruit must be removed and destroyed or ones showing frass-filled holes. Removing infested fruit before the larvae are old enough to crawl out and begin the next generation can be a very effective method for reducing the population. Thinning out the infested fruit has the added benefit of encouraging the remaining fruit on the tree to grow larger. It may also improve spray coverage, if sprays are used.
It is also important to clean up dropped fruit as soon as possible after they fail because dropped fruit may have larvae in them. Removing infested fruit from the tree and promptly picking up dropped fruit from the ground is most critical in May and June, but should continue throughout the season.
Mass Trapping.
Hanging traps in each susceptible fruit or nut tree can help to reduce codling moth populations but won't completely eliminate damage. This method works best where trees are isolated from other trees harboring codling moth (apple, pear, English walnut). It should be used in combination with sanitation and other control methods for the best effect.
Codling moth traps are available from many commercial sources, such as hardware stores, garden centers, or online. These traps usually have a sticky cardboard bottom and are baited with a pheromone (sex attractant) lure. The lure mimics the scent of a female moth, attracting males to the trap. Capturing the males reduces mating and the number of eggs that are laid.
A homemade bait trap generally includes a 1-gallon plastic milk jug containing the following: 1 cup cider vinegar, ⅓ cup dark molasses, ⅛ teaspoon ammonia, and enough water to make 1½ quarts of liquid. Cut a 2-inch diameter hole just below the shoulder of the jug. Leave the cap on the jug. The jug is hung in the tree using a wide strip of cloth to disperse the weight of the jug and protect the tree branch. As an attractive food source this trap will capture both male and female moths. While research is not available on the effectiveness of these traps, backyard gardeners have reported success with this method. Up to 3 of these bait traps can be used per large tree and can be used in combination with the other bait and pheromone traps in the same tree to maximize capture.
Trunk Banding.
A traditional, nonchemical method for controlling codling moth is to trap mature larvae in a cardboard band as they climb the trunk seeking a place to pupate. Banding works best on smooth-barked varieties such as Red Delicious apple, which don't provide good alternative pupation sites; scaly-barked varieties like Newtown Pippin and most types of pears have so many crevices on the trunk that many larva will pupate before they get to the banded area. Even in the best situations, banding will only control a very small percentage of the codling moths because many pupate elsewhere on the tree or in the ground. This is the least effective of the nonchemical control measures and is best used as a supplement to sanitation and mass trapping to help reduce very high populations.
Bagging Fruit.
Control can also be achieved by enclosing young fruit in bags right on the tree to protect them from the codling moth. This is the only nonchemical control method that is effective enough to be used alone and in higher population situations. However, it is quite time consuming to apply the bags so this method is most manageable on smaller trees with fewer fruit. One may bag all the fruit on the tree or just as many fruit as may be needed. However, any unbagged fruit is likely to serve as a host and increase the pest population so it would be prudent to employ sanitation and mass trapping to keep the population in check. Bagging should be done about 4 to 6 weeks after bloom when the fruit is from ½ to 1 inch in diameter. This technique won't affect the maturity or quality of the fruit, but it will prevent full color development on red varieties. Therefore, some bags should be opened to check for ripeness as harvest time approaches. The bags must be re-closed if the fruit is not ready to harvest to keep them protected from codling moth attack. Other benefits to bagging include protection from sunburn and larger fruit as a result of diligent thinning.
Biological Control.
Although a few predators such as spiders or carabid beetles may feed on codling moth larvae or pupae, naturally occurring biological control is not effective. In commercial orchards, releases of the tiny wasp, Trichogramma platneri, has been used successfully to manage codling moth in combination with mating disruption or soft pesticides, but this method has not been tested in backyards.
Chemical Control.
Various chemicals and pesticides have been used in the past, but in addition to being toxic, the prime difficulty in dealing with codling moth infestations using chemicals seems to lie with appropriate timing. The method of calculating ‘degree-days’ is often used by orchardists to approximate when a particular pest will reach a particular stage of development during a given season. Since stages of insect development are triggered by the accumulation of a certain amount of heat over time, this calculation involves careful tracking of changes in daily temperature. In the case of codling moth, adults emerging from pupae in bark and other overwintering spaces will mate and begin laying eggs soon after petal fall. For a given moth, this migration can take place within a mere two to three hours. Effective control using any method therefore depends crucially on identifying when decisive moments such as these occur.
Traps.
The inventor is aware of at least one mechanical trap for codling noths: a Pheromone using trap which lures male codling moths inside. Once inside they will get stuck on the inserted glueboard. Once trapped they are not able to mate with females which will effectively decrease codling moth development in any orchard. Traps are weatherproof and will last several months. However, the pheromone is only active for about 1 month so the whole trap should be replaced monthly. Traps are generally placed in the tree. The moth has thus already entered the tree when the trap becomes effective.
There is a need for a means for controlling codling moths in a way which attracts the moths away from the trees to be protected and in a manner which is efficient and requires the least amount of maintenance.